Airborne sonar systems include a hoist mechanism carried in a helicopter, a storage drum, and drive means therefore which operate to lower a sonar transducer into the water and raise it out of the water. When raised, the transducer is carried snugly against a conical seat which prevents it from swinging or moving during flight. Although the hoist mechanism is operated at limited speeds, there are problems connected with various aspects of the retrieval. One such problem is that the cable tends to carry a substantial amount of sea water with it as it is reeled in. Since the hoist is within the helicopter and since the water tends to be sprayed all around as the cable passes over the guide sheaves, it has been found necessary to provide a cable wiper to prevent excessive amounts of water from being carried on board the helicopter.
With the advent of later types of airborne sonar, transducer operating depths have become much greater, and cable speeds upon deployment and retrieval have also become much greater. While the cables themselves are smaller in diameter, the greater speed results in their carrying even greater quantities of water, at least on a per-unit-of-time basis. With the greater reeling speed and the quantity of water carried it was found that, in the absence of a cable wiper, the spray of sea water as the cable made contact with the guide sheave was intolerably heavy.
A cable wiper design was developed a number of years ago which became the subject of a U.S. Pat. No. 4,132,973, to Myrl E. Orme, common assignee. This design was quite effective in stripping the water away from the cable and keeping it out of the helicopter. In use, however, it was determined that swinging of the transducer in air during retrieval was imposing severe side loading on the wipers, wearing out the wipers in a relatively short time, necessitating frequent replacement. Also, certain parts of the wiper assembly were quite expensive to fabricate. There is, therefore, a need for a cable wiper which is as effective in removing water from the cable as the earlier design, but which has appreciably longer wiper life and which is somewhat less expensive to produce.